The long-term goal of our research is to gain a better understanding of the molecular controls regulating homeostasis of hematopoietic cells. This research proposal focuses on the MyD118/Gadd45/CR6 gene family, which plays a role in negative growth control. The MyD 118/Gadd45/CR6 family members are rapidly induced by genotoxic agents, as well as by terminal differentiation and apoptotic cytokines, and the proteins encoded by these genes play pivotal roles in negative growth control. Examination of hematopoietic tissues in both MyD118 null and Gadd45 null mice revealed increased cellularity, enhanced survival and an increase in the proportion of immature cells. Deregulated expression of MyD 118/Gadd45/CR6 in myeloid cell lines appeared to accelerate the terminal differentiation program and its associated apoptosis. Our working hypothesis is that MyD 118/Gadd45/CR6 play a role in regulating homeostasis of hematopoietic tissues by modulating both the cell cycle and apoptosis; alterations in expression of MyD118/Gadd45/CR6 will modify cell cycle controls and survival, but also will manifest itself by changing the distribution of different lineages and stages of maturation of hematopoietic cells. The specific aims of this research proposal are: AIM 1: Analysis of loss of MyD118/Gadd45/CR6. Mouse strains that are null for MyD118 and Gadd45, and heterozygous CR6 null mice have been generated. The consequences of blocked expression of MyD118/Gadd45/CR6 within the hematopoietic compartment will be assessed, in vivo and in vitro, in both short term and long term cultures, as well as in response to TGFb, and to stress. The effect of loss of MyD118/Gadd45/CR6 expression on the ability to cooperate with oncogenes c-myc, c-myb, E2F-1 or ras, to alter growth and/or differentiation of primary BM will be determined. AIM 2: Analysis of deregulated expression of MyD118/Gadd45/CR6. Hematopoietic cell lines that express inducible deregulated MyD118/Gadd45/CR6 have been established to dissect the role of MyD118/Gadd45/CR6 in growth and differentiation, as well as in response to stress and TGFb. AIM 3: Analysis of the role for MyD11S/Gadd45/CR6 in apoptotic pathways, using cell free systems. Cell free systems will facilitate deciphering apoptosis, and provide an adjunct avenue of investigation to analyze the functions of MyD118, Gadd45, and CR6, as well as interacting proteins, where we can focus on apoptosis, segregated from cell cycle arrest. These investigations should contribute to a greater understanding of the genetic events involved in the pathogenesis of different leukemias and the response to chemo- and radiation therapy, ultimately aiding in diagnosis, prognosis and therapy.